The nation's weather

Weather Underground Forecast for Tuesday, September 18, 2012. An intense storm in the eastern third of the country will drive the most active weather in the country on Tuesday. The storm will begin the day over the South before moving fairly quickly northeastward. It will end the day over Quebec as a major eastern Canadian storm. This storm will have a tremendous amount of moisture associated with it as at least part of its moisture will begin as a tropical disturbance in the Gulf of Mexico. This moisture will translate to ample rain for much of the country east of the Mississippi River. Several inches of rain are expected throughout the Appalachian Mountains in the morning before transitioning in the afternoon and evening farther east along the East Coast from Virginia through Maine. Along with the intense rain, the Storm Prediction Center has warned of thunderstorms and the possibility of tornadoes along the eastern seaboard. The bottom line is that very active and wet weather is expected Tuesday mainly from the Appalachian Mountains to the eastern seaboard. Residents in the eastern third of the country should monitor local weather conditions, especially when it comes to flooding.

Farther to the north, cool Canadian air will spill into the Upper Midwest and eventually the Mississippi Valley. This air will make it feel like Autumn in the Great Lakes area, instigating Freeze Watches in northern Minnesota and adjacent areas of Wisconsin.

Dry conditions are anticipated through much of the rest of the country, with temperatures in the Southeast expected to be in the 90s and some 100s.

The Northeast will rise into the 60s and 70s, while the Southeast will see temperatures in the 80s and 90s in the warmest areas of Florida. The Southwest will rise into the 90s and some 100s, while the Northwest will see temperatures in the 70s and 80s. Temperatures in the Lower 48 states Monday have ranged from a morning low of 24 degrees at Stanley, Idaho to a high of 98 degrees at Imperial, Calif.